Digital terrestrial broadcasting makes transmission parameters such as a modulation scheme and a code rate of inner code variable using a TMCC (Transmission and Multiplexing Configuration Control) signal, thereby enabling hierarchical transmission. For this reason, a conventional digital broadcasting receiving apparatus makes a decision as to whether there is any receivable digital broadcasting signal in a certain frequency band depending on whether the TMCC signal is present or not. However, to decide as to whether the TMCC signal is present or not, a problem arises of taking a time to make the decision because of the necessity for establishing synchronization of the TMCC signal.
To solve the foregoing problem, a conventional digital broadcasting receiving apparatus is known which has a signal level detecting means for making a decision as to whether the signal level of the data output from a data demodulation means for demodulating a received signal is smaller than a predetermined threshold or not, and which selects the next channel at once when the signal level of the data is less than the threshold (see Patent Document 1, for example).
In addition, a device is known which has an analog broadcasting detecting means for detecting the video carrier and audio carrier of an analog broadcasting signal, and a digital broadcasting signal detecting means for dividing the band into several bands, for calculating signal levels in the respective bands, and for making a decision as to whether the difference between the highest and lowest levels among the calculated signal levels is within a prescribed range; and which decides the received signal with the analog broadcasting detecting means, selects the next channel at once when the signal is an analog broadcasting signal, and decides, when the signal is not an analog broadcasting signal, the signal with the digital broadcasting signal detecting means (see Patent Document 2, for example).
Furthermore, another device is known which has the signal level detecting circuit described in Patent Document 1, the analog broadcasting detecting means and the digital broadcasting detecting means described in Patent Document 2, and which causes the analog broadcasting detecting means, signal level detecting means and digital broadcasting detecting means to make a decision as to the received signal in this order (see Patent Document 3, for example).
Patent Document 1: Japanese Patent No. 3538056.
Patent Document 2: Japanese Patent Laid-Open No. 2003-69907.
Patent Document 3: Japanese Patent Laid-Open No. 2006-24994.
The conventional digital broadcasting receiving apparatuses are configured as described above. As for the apparatus described in Patent Document 1, since the analog broadcasting signal has certain power, it makes a decision as to whether the TMCC signal is present about the analog broadcasting signal as well. For this reason, it has a problem of being unable to reduce the search time so much. In addition, as for the apparatus described in Patent Document 2 or 3, since it requires a dedicated tuner for detecting the analog broadcasting signal, it has a problem of becoming larger. Furthermore, since it divides the band into several bands, calculates the signal levels in the respective bands, and makes a decision as to whether the received signal is digital broadcasting signal or not depending on whether the difference between the highest and lowest levels among the calculated signal levels is within the prescribed range, a problem arises of erroneously detecting the noise produced by equipment used simultaneously as the digital broadcasting signal if the noise has certain power in the band.
The present invention is implemented to solve the foregoing problems. Therefore, it is an object of the present invention to provide a digital broadcasting receiving apparatus capable of carrying out search operation at high speed by distinguishing the digital broadcasting signal from the other signals accurately in a short time.